About 15 minutes into this week’s aeronautical drama, “Flight,” as Denzel Washington is calmly, but determinedly instructing his co-pilot and head stewardess in helping him to completely invert the out-of-control passenger jet he is piloting, I thought, “Wow. This movie is going to be good.”

And, for the duration of the doomed flight, the gut-wrenching, edge of your seat, upside-down plane ride that you saw glimpses of in the trailer, the movie is great. Spectacular, almost. I laughed, I cried, I was terrified, and ultimately sank back in relief. The first 20 or so minutes of “Flight” has everything a great dramatic thriller should have.

Unfortunately, there’s roughly two hours of movie left to contend with.

The movie tells the tale of Denzel’s Whip Whitaker, a veteran pilot on the verge of losing it all. Booze and drugs led to a divorce, and now his life consists of a series of alcohol soaked one-night stands, often with a similarly addicted stewardess, in airport hotels, followed by long flights to distant cities where he can do it all again. Whitaker is a man with a problem, and just about everyone around him knows it. But when he gets into the cockpit on that fateful day and huffs a little pure oxygen to clear out the cobwebs, he’s all business.

Except that he isn’t. After a little “hair of the dog” in the form of a couple of mini-bottles of vodka, Whip sacks out for a good part of flight. It’s only when a catastrophic mechanical failure sends his plane into a dive does the real Whip show up. That Whip is a masterful pilot, and, most impressive, unflappable under pressure. Unfortunately, this is the last time we see that Whip.

The rest of the film deals with the aftermath of the crash and the remarkable way Whip saved the plane, the crash landing resulting in only six fatalities instead of the deaths of the entire 102 people on board. As the National Transportation Safety Board begins to investigate, it becomes immediately obvious that Whip had alcohol and cocaine in his blood. The lawyers and the union assure Whip that they can smooth this over, that he’s a hero, but that he has to stop drinking immediately. This proves easier said than done, and that’s when you realize that this is not a movie about flying or pilots, but about alcoholism, replete with AA meetings, sponsors, sincere attempts at sobriety, relapses, and redemptions.

To be sure, this is worthy material for a movie, but not really what the trailer promises.

That the film is somewhat misleading in the marketing isn’t really the problem, however. Director Robert Zemeckis, an incredibly skilled filmmaker, also tends to be very heavy handed. Think about “Forrest Gump,” a movie that works so well because it’s kind of a fantasy. There’s nothing subtle about it.

“Flight” takes a similar route, but one that the audience isn’t as willing to follow. The binges are huge, and often stretch the bounds of suspension of disbelief. Many of the characters are flat — almost archetypes. The slick lawyer, the back-slapping southern airline owner, the damaged drug addict. There’s very little character development in the film, including that of Whip, despite the admittedly masterful performance Denzel turns in. Zemeckis refuses to give us anyone to like in the film, anyone to latch on to and root for. Whip is a fairly odious person, even though we assume there must be something in there that was at one time likeable.

The love-interest, for lack of a better word, Nicole, is so weak and wispy that when she finally exits stage left, you barely notice. Bruce Greenwood and Don Cheadle, as Whip’s best friend and his lawyer, respectively, seem likeable enough, until Zemeckis uses them as whipping boys for his sharp critique of the pilot’s union, which will apparently fight tooth and nail to keep a falling-down drunk in the pilot’s seat, so long as it maintains their hold on power.

What the movie doesn’t spend enough time on, unfortunately, is the character of Whip himself, despite his being in almost every scene. Beyond knowing the basics of his family history, we never really learn much about the man. Zemeckis wanted to tell a broad stroke story about the struggles of an alcoholic, but the genius of the first part of the film hints at a much more interesting story inside that doesn’t get told. We are never told why it is that Whip is such a good pilot. Isn’t this the central question of the movie, and the film’s most poignant potential tragedy? If this character is such a wreck in all other parts of his life, but such a master in the cockpit, even when drunk and high, shouldn’t we learn about his passion for flying, about the ways it straightens him out, about his love for it, and about the incredible loss it would be if he couldn’t do it any more?

Apparently not. These aspects of Whip’s life are skipped over in favor of booze-filled tirades and trippy soliloquies from cancer patients.

Zemeckis obviously wants to tell a cautionary tale about the dangers of alcohol abuse, but, being Zemeckis, he can’t resist a zany character and a great soundtrack. The result is possibly the most off-putting and atonal part of the entire film, the character of John Goodman as the wacky comic-relief drug dealer Harling Mays. As written, Mays is the most capable, most in control, and most rational character of the film. He’s also the one truly likeable character. And if that weren’t enough, he has his own theme song, the sultry sounds of The Stone’s “Sympathy for the Devil” following him wherever he goes. There’s more of that subtlety for you.

But Robert Zemeckis can’t have it both ways. Mays is obviously his favorite character, and his comedic tone completely undermines the rest of the story. There are moments of brilliance in the film. Heart-wrenching scenes peppered here and there, but they never come together to beat out the bombast of the majority of the rest of the movie. It never gets better, or even anywhere close to as good as, the first 20 minutes. Ironically, it’s the crash that soars — the rest of the “Flight” is depressingly earth-bound.